Enantioselective Aldol Related-Reactions Catalyzed by Organic Oxides

This paper reviews enantioselective aldol-related reactions catalyzed by organic oxides (e.g., phenoxides, N-oxides, phosphine oxides, annulenones) developed in the author's group. Chiral phenoxides catalyze the aldol-Tishchenko reaction, the 1,2-addition of an acetylide to a ketone, and various types of Michael addition. Chiral N-oxides or phosphine oxides catalyze aldehyde allylations and aldol reactions involving tetrachlorosilane as the silylating reagent, as well as α,α- and α,α'-double aldol reactions, which are used to realize the short syntheses of some biologically active compounds. The use of trichlorosilyl triflate as a silylating reagent was found to improve reactivity, thereby promoting the intramolecular aldol reactions of ketones as aldol acceptors. The ring opening of meso-epoxide, which generates a chiral chlorohydrin from an achiral starting material, is catalyzed by a chiral N-oxide, phosphine oxide or annulenone derivative.